A standard six-high rolling stand of the type used for rolling strip steel has a pair of vertically spaced nip-defining working rolls of relatively small diameter. Respective upper and lower inner backup rolls of larger diameter bear respectively down and up toward the nip on the respective working rolls, and respective upper and lower outer backup rolls of still larger diameter bear toward the nip on the respective inner backup rolls. All the rolls are carried on journal blocks and those of the working rolls and maybe of the inner backup rolls also, are axially slidably mounted in guide elements that are vertically displaceable in the frame, the blocks of the outer backup rolls normally being carried directly on the edges of the windows of the frame. In addition the roll axes are normally all parallel and coplanar, perpendicular to the workpiece travel direction.
In copending patent application Ser. No. 352,520 filed Feb. 26, 1982 a rolling stand of the above-described type is disclosed, but wherein the inner backup rolls are axially displaceable in the guide elements. Vertically effective actuators can exert a force at least generally parallel to the planes between each journal block and the frame to bend the inner backup rolls and this force can be displaced axially relative to the journal blocks.
In order to use the smallest possible diameter of working roll, so that maximum pressure can be brought to bear on a particularly hard, thin, or wide piece of strip, it is furthermore known to laterally brace these working rolls. This is done as described in pages 309-314 of Herstellung von kaltgewalztem Band (Verlag Stahleisen, Dusseldorf; 1970) by providing lateral bracing or backup rolls bearing against the downstream side of the working rolls. In this type of setup the working rolls are normally centered on axes slightly downstream relative to the workpiece travel direction from the plane of the backup-roll axes. The pressure exerted in the upstream direction opposite the workpiece travel direction can be varied over the length of the working rolls to keep them from bowing to a shape concave upstream.
In fact the standard roll stand can operate with working rolls whose diameter varies at least about 50 mm, as this much change in size occurs normally since a working roll is periodically turned down a little to eliminate worn spots and return it to perfect cylindrical shape. Nonetheless, accommodating working rolls that do not lie within this range requires a substantial rebuilding of the stand. In fact such a changeover can take two entire shifts, resulting in a substantial loss of production.
Moreover, it can be necessary, depending on the type of hot- or cold-rolling being done, to operate a single stand with, for instance, only two 900 mm long and 900 mm-diameter rolls. For another application four-high operation with 420 mm-diameter working rolls can be needed, or six-high operation with working rolls from 140 mm to 165 mm. With lateral bracing the working-roll diameter can sink to 52 mm to 57 mm. Converting the stand for such wide variation in size of working roll remains a very complex and time-consuming task. Even so-called convertible stands require major reassembly to accommodate such a wide range of sizes, which are accompanied with the smallest working rolls that must be laterally braced by a downstream shift of the position of the working-roll axes from the plane of the backup-roll axes, so that the changeover is very complex.